The present invention relates to a discharge head lamp assembly of projector type for a vehicle.
A head lamp assembly of the kind referred to above comprises a lamp housing having a front face formed therein with an opening. A reflector and an electric discharge lamp are housed within the housing, and the discharge lamp is arranged substantially in a focus position of the reflector. An inner lens made of a glass material converges a light from the discharge lamp and the reflector to illuminate a location in front of a vehicle. A shade is arranged between the inner lens and the reflector. The opening in the front face of the lamp housing is covered with an outer lens. The outer lens is made of a resinous material in order than an attempt is made at lightening or reduction in weight. A location between an outer peripheral portion of the inner lens and a front face of the outer lens is covered with a blindfold inner panel or finisher, so that the interior of the housing cannot be seen from the outside through the outer lens.
Since the head lamp assembly constructed as described above uses the discharge lamp high in luminance and long in service life, an attempt can be made to reduce, in size, the lamp per se and to lengthen the service life thereof. Further, a shadow formed by the shade is projected toward a location in front of the inner lens, thereby making a cutline or a light-and-dark boundary definite. Thus, there is obtained a characteristic of a luminous intensity distribution of a (downward) dimmer beam in which there is substantially no upward leak light.
In the discharge head lamp assembly constructed as described above, however, a large quantity of ultraviolet rays is discharged from the discharge lamp. Although the ultraviolet rays can partially be removed or reflected by the glass inner lens, all the ultraviolet rays cannot be removed. Thus, there is a case where the resinous outer lens changes color or is discolored by the ultraviolet rays passed through the inner lens, and cracks occurs in the resinous outer lens by the ultraviolet rays transmitted through the inner lens.